Modulated electron discharge device



y 1957 G. H. ROBERTSON 2,798,203

, MODULATED ELECTRON DISCHARGE DEVICE Original Filed April 5. 1952FEQBOMAGA/ET/C MA TEE/AL //v VEN r02 6. H ROBERTSON A TTORNE V UnitedStates PatentO MODULATED ELECTRON DISCHARGE DEVICE George H. Robertson,New Providence, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York Originalapplication April 5, 1952, Serial No. 280,707, now Patent No. 2,691,765,dated October 12, 1954. Divided and this application February 12, 1954,Serial No. 409,806

8 Claims. (Cl. 332-51) This invention relates to electron dischargedevices and more particularly to such devices of the traveling wave tubetype. c I

This application is a division of application Serial No. 280,707, filedApril 5, 1952, now Patent 2,691,765, October 12, 1954.

Traveling wave tubes generally comprise a transmission line, whichdefines an interaction circuit, and a means for projecting an electronstream along that interaction circuit. In one known type of travelingwave tube, the interaction circuit comprises a helix to which the highfrequency carrier wave is coupled; in other types of traveling wavetubes, the region of interaction may be defined by a filter-type circuitor by resonators. Amplification in these tubes occurs due to theinteraction of the electromagnetic waves associated with both-the helixand the electron stream in the vicinity of this interaction region.Priorly, the high frequency carrier wave hashad the modulating signalapplied thereto, external to the traveling wave tube, so that it is themodulatedcarrier that is introduced to the traveling wave tube andamplified thereice the material under the control of the modulatingsignal. In this manner the attenuation applied to the interactioncircuit is varied under control of the modulating signal to decrease theamplification in accordance with the modulating signal, whereby thecarrier wave is amplitude modulated.

It is a feature of this invention that attenuation be provided in atraveling wave tube by a magnetized element of a ferromagnetic materialencompassing the interaction circuit but distinct therefrom.

It is a further feature of this invention that attenuation in atraveling wave tube be provided by a solid hollow magnetized element ofa ferromagnetic material encompassing the path of the electron stream inthe traveling wave tube.

It is another feature of this invention that the ferromagnetic elementbe magnetized to be near its ferromagnetic resonance in the frequencyband of the signal to be amplified.

It is still another feature of this invention that the attenuation ofthe traveling wave tube be varied by an externally applied signal byvarying the magnetic field through the magnetized element in accordancewith the externally applied signal.

A complete understanding of this invention and of these and otherfeatures may be gained from consideration of i the following detaileddescription together with the acin. This, of course, requires that thesteps of modulation and amplification be distinct, employing separateapparatus and interconnections therebetween.

In accordance with an aspect of this invention, a high frequency carrierwave, such as may be derived from a crystal controlled oscillator, isdirectly introduced into a traveling wave tube and the modulating signalapplied to the carrier within the tube itself. In a specific embodimentof this invention, this is attained by varying the attenuation of theinteraction circuit under the control of the modulating signal.

The amplification or gain of a traveling wave tube depends on thecharacteristics of the wave associated with the interaction circuit, e.g., with the helix in one known form of tube, and the interaction ofthat wave with the electromagnetic wave associated with the electronbeam. Priorly, loss has been applied to the helix or positioned adjacentthereto to attenuate the electromagnetic wave associated with the helixso that feedback due to the signal being reflected back from the outputwill not occur. In accordance with a feature of this invention aferromagnetic member distinct from the helix or interaction circuitencompasses the interaction circuit and provides attenuation in thetraveling wave tube. This ferromagnetic member is magnetized andadvantageously in accordance with an aspect of the invention ismagnetized to be near companying drawing, in which the single figure isa sectional representation of a traveling wave tube illustrative of onespecific embodiment of this invention.

Referring now to the drawing, the specific embodiment et this inventiondepicted comprises an envelope 10,

which may be of a conducting material and in which are positioned acathode 11, heater element 12, and accelerating electrode 13, definingan electron gun, an electron receiver 14, and a helix 15. The ends ofthe helix 15 are brought out through coaxial input and output terminals17.

,, having flanges 21 at each end encompasses the cathode 11, controlelectrode 13, helix 15 and collector electrode 14, leads being broughtfrom the end of the helix 15 through apertures 22 in the cylinder 20 tothe coaxial terminals 17. External to the envelope 10, which is of anon-magnetic material, is positioned a long U-shaped core member 24having its depending portions 25 facing the end flanges 21. The core 24need only be a segment of a cylinder, or an approximation thereof, andone or several may be employed. A coil 27 is wound around a portion ofthe core 24, an identical coil being thus positioned for each coreutilized. A voltage source 28 and the secondary 30 of the transformer 31are in series with the coil 27. The core 24 may be of a permanentmagnetic material or of a ferromagnetic material, such as ferrite, witha superimposed direct magnetic field in either case. The field strengthproduced by the permanent magnet and/or the coil 27 in the ferritecylinder 20 is adjusted so that ferromagnetic resonance occurs near thefrequency band of the signal to be amplified, the occurrence offerromagnetic resonance being dependent on both field strength andfrequency. Near the ferromagnetic resonance of the ferrite, the loss inthe ferrite will change rapidly with the field strength. For a narrowband of frequencies to be modulated, this variation in the ferromagneticloss, and thus in the attenuation coupled to the carrier wave, can becontrolled by a modulating signal 33 applied to the transformer 31 tovary the magnetic field in the magnetic circuit of the cylinder 20 andthe core 24 and thus modulate the carrier.

As the ferrite cylinder 20 entirely encompasses the helix 15 it shouldalso be utilized to provide magnetic chosen, so. that-itsiferromagneticresonance. occurs, at a.

value of field strength-at. least. sufficient torfocusdhe elcc-- 'tronstream.

Modulating. the carrier wave by thisspecific. illustrative embodiment ofthis. invention. other than, by theaother embodiments set forth in theparent application can. best beutilizedfor relatively low modulating;frequencies at. which. the hysteresis etfectswithin-the. ferromagneticcylinder 5.0 will not be, a limiting factor..

While this invention hastbeendescrihed-with referenceto modulationofthe-carrier wave-.in;accordancewith-a modulating signal,.i.t;is tobeunderstoodjthat the impedi ance" value of} the variable,- impedance:elernenttinzenergy, coupled: relationship: may be; varied tov vary the;attenun ation at a given point or along the interaction circuit;inaccordance; with. other-than: modulating; signals... Sim: ilarly,although the; specific;-embedirnentaofithisiinvention. described abovehas,inc.or.p.orated.a helix as. defining the; interaction circuit, thisinvention is equally applicabltc to ether types .of traveling-wave.tubes wherein the electromagnetic wave'may be; slowed downinothergmanners. and the region. of interactionv thusdefined by. otherstruc tures, such as. by filter-type circuits. or. resonators. N r. isthis invention to be considered limitedll-to, the manner; of.introduction of the.- carrier wave-inttx-the; device; as this willdepend on anumbercf considerations; such: as: carrier frequency. Thusthe carrier; wave. may be; con: pled to the; interaction circuit. not:only. by coaxiai tor: minals, but by wave. guides, resonatorsrgridstelectron. streams, or in othergmanners knowninthevart...

Further, this invention. is not: limited to:- the inclusion with themagnetized ferromagnetic attenuating'memher of elements to vary thevattenuation ofztheiferromagnetic. member.

Itis tobe understoodthat the ahoveadescribed;arrangements areillustrative of. the-application. of the: principles. of this invention.Numerous; other arrangements, maybe devised by those skilled in the artwithout departing: from the; spirit and scope of; the invention.

What is claimed is:

1. An; electron discharge. device; comprising-:mcans. for. propagating atraveling. electromagnetic wave; along; an. extended path, mcansfor,projectinga streantof; electrons along said. path, means. distinct.from; said propaga ing means. for providing. attenuation along: said.path. said:

attenuation means including-fa. magnetized; element: of:

ferromagnetic material encompassing: said: path. anti-in: energy coupledrelationship. with the.electromagnetictfieltl;

of said wave, and means for; applying-1 11 magnetic. field to saidelement. such that. the magnetic field strength;

along said path issufficient to, focus said; electron; strearnt.

2. An electron discharge device. comprising; means. for propagating atraveling electromagnetic wave along. an extended path, means for,projecting a stream; of electrons. along said path, means forprovidingattenuation along said path, said last-mentioned. meansincluding a solid; hollow magnetized element of ferromagnetic. materialencompassing said path, and means applying; a magnetic. field to saidelement to focus saidelectron; stream, whereby said hollow element.both. provides. said. attenuation and serves as a flux. guide. for. thefocusing magnetic. field.

3. A, traveling wave tube comprising electrical con: ductor meansdefining an interaction circuit, means for projecting a stream ofelectrons along said circuit, means for introducing a carrier wave tosaid circuit, and means for providing attenuation of said wave alongsaid circuit, said last-mentioned means including a magnetic memberencompassing said-conductor and means for magnetizing said magneticn1embe r,. said, magnetizing, means. includingmeans for-providingaisufilcient field strengthin said member for focusingsaidelectronstream.

4. A traveling wave tube in accordance with claim 3 wherein saidmagnetic member is of, a ferrite material.

5. A traveling wave tube in accordance with claim 3 wherein said'meansfor magnetizing said magnetic member comprises means for providing amagnetic field strength in said member-such that. said'member is nearferromagnetic resonance.

6. Anaelectron discharge. evi cmpr singmeans defining -;an. interaction.circuit, me ns. f prei ting. a

stream of electrons along said circuit, means for; intro-.

ducinggalcarrier; wavete said; circuit, n me n for: ying the amplitude;oh said carrier; wave, saidlast-mentioned means comprising a firstmagnetic element having a variable, ferromagneticloss characteristic inenergy coupled relationship-with. the electromagnetic field, of

said carrier, fl2SC Ildt i gI1Q element. a j n id: fir magneticelement-and; defining; a magnetic; circuit therewith,;and; means-forvarying themagnetic field strength in said magnetic, circuit to;vary-the.- ferromagnetic loss, insaidfirst. magneticelementi' 7'.Anelectron discharge deyice-compr-ising means defining an; interaction,cir uit-cmeansfor: projectinga stream of; electrons.v along saidcireuiti means f r. introd cing a carrier: Wave to, said cireuit,and'means, for; varying the attenuation along said circuit,saidlast-mentioned meanscomprising; at ferrite; member having avariable, ferromagnetic lossmharacteristicnfiarferromagnetic resonance,saidferrite mom-hen being adjacent said circuit, a,magnetic"memberaadjacent,said ferromagnetic member; and defining amagnetiocircuit therewith, means for providing a magnetic field,strength. in said magnetic circuit such thatsaildrfenritei member. is;near: ferromagnetic resonance, anti-means for;-varying-said fieldstrength.

8. An electron, discharge, device; comprising means definingan-;interactioni circuit-,electrOn gunmeans for projecting.astreanr-of'electrons along said circuit, meansforintrodncingacarrierwayejto said; circuit; and. means for: varying the. attenuation.along said circuit, said last-.

References; Cited in the-file. of this patent UNITED STAT ES PATENTS2,197,123 King; Apr. 16, 1940 2,602,148 Pierce July 1, 1952 2,629,079Miller etal. Feb. 17, 1953 2,645,758 'Lindt" July 14, 1953.

